1. Field of the invention
The present invention relates generally to an automatic focusing apparatus having a function of chasing or tracking an object, and more particularly to the apparatus to be utilized for automatic focus-adjusting of a photographic lens of a video-camera and a camera having a function of an automatic focus adjustment.
A conventional automatic focusing apparatus for use in a video-camera is generally of a type that a focusing zone thereof is unchangeable, so that the focus adjustment of the photographic lens to an object to be photographed is impossible when the object is beyond the corresponding focusing zone, and accordingly much more inferior picture images are produced so far. In order to avoid such disadvantage, there has been provided a method of changing the focusing zone depending upon a photographer's intention. However, shifting of the focusing zone by manual operation induces troublesomeness, and furthermore it happens to induce not only unconcentration of photographing but also misjudgement of shifting the focusing zone.
For example, Japanese Laid-open Patent Publication No. 146028/1984 discloses an apparatus for automatically shifting the focusing zone, which is described hereinbelow.
The apparatus is provided with a plurality of focusing zones. One distance measuring data, which is one of distance measuring data corresponding to the shortest distance between the photographic lens and the object, is selected out of some of distance measuring data corresponding to each focusing zone in order to bring the object located closest to a photographer into in-focus position In this prior art, it is ensured to chase the object automatically only when the object to be photographed is located closest to a photographer. However, if another object exists between the photographic lens and the object to be photographed, that is, if another object is located closer to the photographer than the object to be photographed is located, the focus adjusting operation must be done as to said another object, so that it is not ensured that the focus adjusting operation can not be carried out as to the object to be photographed.
In photographing a movable object, such as a person who is playing sports, using the video-camera, it is desirable that the automatic focus adjustment is carried out as chasing the object automatically. In the automatic focusing apparatus by which the focus adjustment of the photographic lens as to any one selected out of a plurality of focusing zones can be carried out, there may be available such a method in which the focus detection is preferentially carried out as to the focusing zone which has been used at the preceding distance measuring and if reliability of the focus detection on the focusing zone having priority becomes low, another focusing zone is selected assuming that the object has moved to any place. However, the above method still has the following problem. For instance, when a person as the object being in one focusing zone, as shown in FIG. 7A, has moved sideways so that another object, on which the lens can be focused, appears in the background, as shown in FIG. 7B, the focus adjustment must be done with respect to the background as an object and thus, there remains such a disadvantage that execution of the focus adjustment with respect to said person to be photographed is impossible.